Electrical transformer



Oct. 13, 1953 w. N. PARKER ELECTRICAL TRANSFORMER Filed March 11, 1950 Ia v, o I l Ff/11126711112 INVENTOR M/baw NR? 01' ATTORNEY Patented Oct.13, 1953 ELECTRICAL TRANSFORMER William N. Parker, Lancaster, Pa.,assignor to Radio Corporation of America, a corporation of DelawareApplicationMarch 11, 1950, Serial No. 149,044

1 Claim. 1

My invention relates to transformers and particularly to transformersystems supplying power to a load device requiring high operatingcurrent at low voltage.

One instance of a use for such a power supply, and which I shall employto illustrate my invention, is to supply the heating current for thecathodes of high power electron tubes such as are used in radiotransmission.

In such tubes, it is ,common practice to have a number of cathodemembers, all connected in parallel. It is preferable that these cathodemembers be directly heated by the passage of current through them. Thesecathode members are usually relatively short and have a low resistance.Since the resistance is low, a large current is required to produce theheat necessary to maintain the cathodes at emitting temperature.Providing suitable short internal leads of high current carryingcapacity presented a problem. One

solution for this problem was the provision of heavy concentric orcoaxial rings or cylinders of suitable material to which the cathodeswere fastened, such as in the RCA type 5831 tube which is more fullydescribed in copending application Serial No. 81.932, filed March 17,1949.

For eflicient operation, the apparatus supplying the large current tothe cathode leads should follow the same principles as the leadsthemselves. That is, it should be so arranged that the leads connectingthe power supply to the cathode leads are as short as possible andpresent as small a resistance to the flow of the current as is possible.A convenient apparatus for supplying the current required is atransformer.

Accordingly, it is an object of my invention to provide an improvedtransformer.

A further object of my invention is the provision of a transformersystem for supplying a large current at low voltage-wherein the outputterminals are coaxially disposed.

Still another object is to provide a transformer system adapted to beused with high-power electron tubes, particularly with those tubeshaving concentric or coaxial cathode leads.

In accomplishing these and other objects, I provide a transformer havingone or more annular cores of ferromagnetic material. Each of these coreshas a toroidal coil wound upon it. These coils constitute the primary ofthe transformer. The secondary of the transformer comprises a shell ofelectrically conductive material that substantially surrounds theprimary coils. This shell is in the shape of a hollow annulus that isopen at one endand has a substantially U-shaped cross-section. In orderto provide flexibility in the operating conditions of my system, Iprefer the use of several primary' coils. In such case, the ends of theindividual coils may be connected to independent external terminals sothat they may be connected in different ways, depending on the desiredoperating condition.

A better understanding of my invention may be had from the followingdetailed description when read in conjunction with the accompanyingdrawings in which:

Fig. 1 is a cross-section view of an embodiment of the transformer of myinvention.

Fig. 2 is a cross-section view taken along the line 22 of Figure 1.

Fig. 3 shows a modified form of the secondary of the transformer.

Fig. 4 is a fragmentary cross-section view showing another modificationof the secondary of the transformer,

Fig. 5 is a fragmentary View, partly in crosssection, showing thetransformer of my invention connected to the base portion-of ahigh-power electron tube.

Fig. 6 is a fragmentary view in cross-section showing the transformer ofmy invention built into a high-power electron tube, and

Fig. 7 shows in a fragmentary cross-section view, a modification of thetransformer structure.

Referring to the drawings in detail, in Figs. 1 and 2 I have shown aplurality of annular core members I of laminated ferromagnetic material.Wound upon each of these cores is a toroidal coil 2. These coilsconstitute the primary of the transformer. The coils 2 are placed in ahollow annular shell 3. This shell is made of an electrically conductivematerial, such as copper, and serves as a secondary for the transformer.The shape of the shell substantially takes the form of a pair of spacedapart concentric cylinders, the two cylinders being joined at one end.The primary coils and their associated cores are placed in the spacebetween the inner and outer cylinders. A pair of concentric rings 4 and5 is formed by the open ends of the cylinders. These rings are theterminals for the secondary of the transformer. The ends of each of theprimary windings may be connected to individual or independent externalterminals whereby the separate coils may be variously connected, as willbe explained later. V

A modified form of the secondary is shown in Fig. 3. Instead of theone-piece, one-turn secondary shown in the other figures, the cylindersare formed by a number of U-shaped copper straps 8. These straps arehere shown arranged in groups of two and one strap of each group isserially connected to the other by a connecting strap 9. Thus each pairof straps constitutes a two-turn secondary.

The groups of straps are, in turn, connected in parallel to two contactrings l4 and 15. These rings correspond to the terminal rings & and ,5of the shell type secondary shown in Figs. 1 and 2. It may be seen thatthe arrangement shown in Fig. 3 provides a plurality of two-tumsecondary windings all connected in parallel. By eliminating theconnecting strap 9 and connecting the ends of the U-shaped members 8directly to the rings 14 and i5 respectively, a plurality of oneturnsecondaries is formed. A three or more turn secondary may be provided ina manner similar to that shown and discussed in the twoturn arrangement.

A fragmentary view of the base portion of a high-power electron tube [2is shown in Fig. 5. One end of each of a plurality of cathodes (notshown) is connected to a contact flange 16. The other ends of thecathodes are connected to a cylindrical member that extends through thebase of the tube to form a contact ring H. A set of spring loadedcontact fingers l8 provides a convenient means of assuring a goodelectrical contact between the inner ring 5 of the secondary and thecontact ring ll of the tube l2. Suitable clamping devices (9 areprovided to secure the tube to the transformer, the outer ring 4 of thetransformer making direct electrical contact with the contact flange itof the tube.

Under some conditions of operations, the current in the secondary may belarge enough to cause excessive heating of the secondary, To obviatethis, I provide a modified construction of the secondary member in whichthere are intrawall cavities 20, substantially as shown in Fig. 4,through which a fluid coolant may be passed.

When the transformer is used to supply the heating current for thecathodes of electron tubes, it is desirable to be able to control thestarting current since the resistance of the cathodes will varyconsiderably as their temperatures change. I have shown in Fig. 3, onearrangement for controlling the output of the transformer. In thetransformer there shown, I provide eleven identical toroidal primaries2. The

bottom six of these toroids are connected in parallel to a double-pole,double-throw switch 22. One side of the switch 22 is connected to asource of alternating current 26. The other side of the switch 22 isconnected to a shorting bar 25. The top five toroids are connected inparallel to a variable auto-transformer 28. The auto-transformer isconnected through a reversing switch 30 to the source of alternatingcurrent 26.

To initiate the operation of the system, the switch 22 is closed toconnect the bottom six toroids to the source of current 26. Theautotransformer is adjusted so that its output voltage is in a ratio of6/5 with its input voltage. The reversing switch 30 is closed to causethe current in the top five toroids to flow in the opposite directionfrom the current in the bottom six. Since the voltage impressed on thetop five primaries is six-fifths of the voltage impressed on the bottomsix, the voltage induced in the secondary by each set will be equal.However, since the two sets are bucking each other, the net inducedvoltage in the secondary will be zero. Now, if the output of theauto-transformer 28 is reduced, the net voltage induced in the secondarywill increase. The output of the main transformer will be one-half ofits full load output when the output of the auto-transformer 28 is zero.At this point the reversing switch 30 may be closed on its other side.If the output of the auto-transformer is now increased, the current inthe upper set of toroids will be aiding that in the lower set. Thisresults in a transformer whose output is continuously variable from zerooutput to full load while controlling only half of the total powerinput.

It should be understood that the exact number of toroidal primaries hereillustrated is not essential to the carrying out of the foregoingoperation. There may be more or fewer primary coils, with the controlvoltage supplied by the auto-transformer being adjusted accordingly. Ifconditions are such that not more than half of the total power isrequired, the switch 22 may be closed on the shorting bar 25. Thisshortcircuits the lower six primary coils, allowing the upper five coilsto supply the power for the load.

In some instances, it may not be desirable to have the output of thetransformer variable from zero to full load. Instead, it may bepreferable to have the output variable only between certain limits. Insuch case the control voltage from the auto-transformer could be appliedto a fewer number of the primary coils. For example, only one coil maybe so connected.

Other adaptations of the transformer include various combinations ofparallel and series connection between the individual primary coils.These various combinations provide selection among any of a number ofdifferent line voltages that may be applied to the primaries to producea given output voltage.

Although I have shown and described the primaries as having independentexternal terminals, the several primary coils may be connectedinternally in any suitable or desired manner.

While, in most instances, it may be more convenient to have thetransformer separable from the tube with which it is associated, it iswithin the contemplation of my invention to have the transformer builtinto the tube as I have shown in Fig. 6. The glass side wall 33 of thetube is secured to the transformer secondary through a suitableglass-to-metal seal. This arrangement, with nothing more, would providean envelope enclosing all of the tube elements as well as the primarycoils of the transformer. When the envelope is evacuated, the gasabsorbed by the elements in the envelope must be driven off during theevacuating process. The primary coils with their associated cores wouldhave a large quantity of this absorbed gas; and it would ordinarily bediflicult to drive the gas out. However, in order to reduce thedifficulties encountered in degasing such a tube, the main or vacuumchamber of the tube is isolated from the primary coils by means of aseal-off member 35. In such an arrangement, the cathodes 31 mayconveniently be connected directly across the secondary terminals 4 and5.

As I have previously indicated, the resistance of the cathodes isconsiderably-lower when they are cold than when they are heated tooperating temperature. If full load voltage is applied to these cathodeswhile they are cold, excessive current would ordinarily flow through thesecondary circuit. In Fig. 7 I show, in addition to the core members,around which the primary coils are wound, an auxiliary annularferromagnetic core 18. This auxiliary core does not have a primary coilassociated with it, but provides a closed magnetic path in the field ofthe secondary. This introduces sufiicient reactance into the secondarycircuit to limit the excessive current that would flow if the full loadvoltage were applied to the cathodes while they are cold.

From the foregoing, it may be seen that I have provided a new and usefultransformer system for supplying low-voltage, high-current loads. Thesystem is particularly adapted for use with those load devices havingcoaxial or concentric leads.

What I claim is:

A transformer having a plurality of ferromagnetic cores, each of saidcores providing a closed magnetic path, a toroidal primary coil wound oneach of said cores, a secondary for said transated coils being containedin the space between said cylindrical members, independent externalterminals connected to the windings of each 01' said primary coilswhereby said primary coils may be variously connected, and an auxiliaryannular ferromagnetic core, said auxiliary core being disposed withinthe outer one of said cylindrical members and axially displaced fromsaid aforementioned cores, thereby introducing a reactance to limitexceedingly high starting currents in said secondary.

WILLIAM N. PARKER.

References Cited in the file of this patent

